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You plug in your nice new guitar and fire up your amp. As you wait for your tubes to start glowing you hear the fade in of the ever-dreaded hum. What do you do?
The first step is determining what type of noise you have. Is it 60 cycle hum? Is it more of a buzz? Does it get worse or better if you put your hand on the strings or when you touch the barrel of the cable? Have you tried a different cable? Have you tried a different receptacle or setting up in a different location?
Let’s assume you eliminated all the variables and determined that the noise is being generated within the guitar.
The number one cause of hum is environment, and unless you lock yourself with your guitar in a Faraday cage, you will never fully eliminate it. You can, however, mitigate it substantially.The number one cause of hum is environment, and unless you lock yourself with your guitar in a Faraday cage, you will never fully eliminate it.Click To Tweet
This is the most common hum you will hear from your guitar. All the transformers, ballasts, chargers and wall warts in your house / venue emit an alternating electromagnetic field that coincides with your alternating current. All the wiring in your house / venue also emits this magnetic field. Not only that, but these alternating magnetic fields are synced, so you are basically surrounded by this omnidirectional alternating magnetic field. Depending on where you orient yourself within these fields will determine how severe your symptoms are.
This is different than your typical induced hum. It is more of a buzz… This type of buzz is obnoxious and may or may not go away when you touch the strings.
This is the one that can be fixed by checking your grounds. To diagnose, plug your guitar into your amp, but have your amp unplugged from the wall. Take your multi meter and check the resistance between the bridge, electrical components and pot casings of your guitar against the ground pin on your amp’s power cord. You should have a resistance of 1 – 2 ohms between any ground point in the guitar and your amps ground pin. If it’s significantly higher than that, then you may have a grounding issue.
Wifi, Cell phone and other wireless devices.
If you have a cell phone in your pocket while you’re playing, you’ll very often hear a ‘morse code’ like pulsing through your amp right before your phone rings. If you stand near a computer or a wireless router, with your guitar, you will hear a constant ‘tick, tick, tick,’ or sometimes a ‘hum’ that will vary in frequency. You can also hear other noises if it’s positioned just right.
Your pickups are inductors. They don’t discriminate between your strings altering their magnetic field, or an outside EMF altering their magnetic field. Any alteration of a magnetic field within a coil will produce a current, and in a guitar+amp, that current is converted to an audio signal.
Here’s an experiment that will show this. Grab any guitar, and plug it in.
Now, get some audio going through your smartphone or any other portable device with a small speaker. (keep it small)
Hold the speaker side up to your guitar pickup. You will hear the audio from your phone through your guitar amp.
This is not due to microphonics; this is due to your guitar pickup’s magnetic field being manipulated by the magnetic field of your phone’s speaker driver. You are inducing a signal through your pickup.
So why does touching your strings / bridge stop the hum?
Your strings are grounded to the guitars circuit. Your body is conductive. When you don’t touch the strings, your body is acting like an antenna for all the EMF floating around you and can actually CAUSE hum. When you touch the strings, your body is now connected to the guitar and amps ground. You have turned yourself into a shield for your pickups.
Humbuckers are designed to mitigate hum by having two coils wound in opposite directions, with one coil having north magnetic poles and one having south magnetic poles. This will allow any signal received from the string to be in phase, electrically speaking, and pass through to your amp. Any signal the is induced from an outside source will be electrically out of phase between the combined coils, and cancel each other out. You should not have substantial hum with a humbucker equipped guitar.
Properly shielding your guitars pickup cavities can significantly reduce induced hum.
A properly wound dummy coil can virtually eliminate hum, but it comes at the expense of loosing top end.
This is a product that can reduce hum significantly… it’s basically a low impedance dummy coil, giving you the reduced hum without loosing your top end.
Hum Canceling Systems
These work extremely well, but are expensive.
Sometimes the hum has nothing to do with the guitar, it can sometimes be induced in the amps circuitry, or be caused by power / grounding issues in your houshold /venue wiring.